Not even the coldest of hearts can resist a small child XP Shining may be professional around his parents and his girlfriend (who is royalty, so I guess he wnats to make a good impression on that part), BUT his baby sister? Yeah...

Only if Celestia didn't intervene (and there's a good chance she would've because Cadance was already in a relationship with Shining and Twilight herself might've just become Celestia's apprentice at this point).